With the increasing utilization of in vivo mouse models, there is a growing demand for the traditional disciplines of pathology and histology. Proper evaluation of the complex cellular and molecular events that occur in various organs under resting and challenge conditions requires extensive histological analysis. The successful conduct of histological studies depends on an equipment infrastructure and expertise. For optimal tissue processing, the cutting and staining of specific cells has to be done by highly skilled technical personnel to achieve consistent and reliable results. Extensive expertise in microscopic evaluation is critical for designing and interpreting histological studies. NIH has acknowledged in various Congressional Reports, that the great increase in the numbers of genetically altered mice used by the biomedical research community has led to great pressures to keep up with and develop the requisite pathobiology expertise.